1. Field of the Invention
This invention relates generally to a system and method for polling a vehicle key fob to determine when an authorized vehicle user is approaching a vehicle that uses a pulsed polling signal in the VHF-UHF band and, more particularly, to a system and method for polling a vehicle key fob by a vehicle that uses a pulsed polling signal in the VHF-UHF band or polling a vehicle by a vehicle key fob that uses a pulsed polling signal in the VHF-UHF band to determine when an authorized vehicle user is approaching the vehicle.
2. Discussion of the Related Art
Modern vehicles typically include a key fob that wirelessly transmits RF command signals to a vehicle controller to perform certain vehicle functions, such as lock the doors, unlock the doors, open the trunk, open the hatch, start the engine, turn on a security light, etc. The vehicle operator will press a particular push button on the key fob that typically has an image of the function that the button provides in order to transmit the command signal to the vehicle. The transmission is coded in such a manner that not only does the command perform a certain operation, but also protects the transmission from being recorded and resent by a third party. Key fob s of this type typically have a limited range, and provide a convenience factor for the vehicle operator.
Modern vehicles also typically allow a vehicle driver to set various vehicle devices and systems, such as vehicle mirrors, seats, pedals, radio, etc., to a particular desirable setting, and then allow the driver to record those settings as pre-sets by activating a storing button. If the settings are changed from the last time the vehicle driver drove the vehicle, such as by another vehicle driver, then that vehicle driver can activate the pre-sets, such as by pressing the storing button or another button, so that all of the devices are returned to the desirable position for that driver. A signal transmitted from the key fob identifying the vehicle driver can be used to set the various vehicle devices and system to the pres-set conditions, where the particular key fob is unique to the vehicle driver.
Systems have been proposed for a vehicle that cause a vehicle door handle to retract into the vehicle door for security purposes and upon detection of an authorized user will extend the handle to allow the driver to gain access to the vehicle. Current systems that deploy a vehicle handle from a retracted position may require about ten feet between when an authorized vehicle user is detected and when the user arrives at the vehicle to perform the operation satisfactorily.
As mentioned above, a typical system that allows a key FOB to provide vehicle commands is activated by the vehicle driver or other authorized user using the key fob. It is desirable in some vehicle designs to cause the vehicle to perform the particular function automatically as the user approaches the vehicle, where the user is not required to actively transmit the signal. One known system, referred to as a passive entry passive start (PEPS) system, periodically interrogates or polls the area immediately around the vehicle to detect the key fob using a low frequency (LF) pulsed signal (30-300 kHz) transmitted from the vehicle at a predetermined pulse rate. The pulse width and the pulse rate of the polling signal is set based on how fast the user could be approaching the vehicle and how far from the vehicle it is desirable to first detect the user. When the key fob receives the low frequency pulsed polling signal, and authenticates it, the key fob will automatically transmit a command signal to the vehicle so that the vehicle will perform the particular function that is has been programmed to perform.
Low frequency signals are typically used for the key fob polling because they only radiate a short distance. Further, because of the short range of the low frequency pulsed polling signal, it is possible to interrogate directionally, such as at the left or right side of the vehicle or the front or rear of the vehicle. Thus, because the vehicle can know the direction of the approaching user, the vehicle need only open the door for that side.
Generating and transmitting low frequency signals typically requires a large amount of current, typically on the order of about 700 mA, for each pulse that is transmitted. Therefore, the amount of time that the vehicle is able to provide the pulsed polling signal at the low frequency before the vehicle battery voltage is reduced to an unacceptable state-of-charge, below which the driver may not be able to start the vehicle, is relatively short, for example, on the order of 12-24 hours. When this time has passed since the last time the vehicle was started, the PEPS system will go into a sleep mode, and not be able to provide the polling signal.